1. Field of the Invention
This invention relates generally to methods used to complete and produce hydrocarbons from subterranean wells and more particularly relates to apparatus and methods for regulating production along the length of a completed zone to optimize the production and ultimate recovery from the reservoir.
2. Description of Related Art
Hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation, referred to as a reservoir, by drilling a well that penetrates the hydrocarbon-bearing formation. Once a wellbore has been drilled, the well must be completed before hydrocarbons can be produced from the well. A completion involves the design, selection, and installation of equipment and materials in or around the wellbore for conveying, pumping, or controlling the production or injection of fluids. After the well has been completed, production of oil and gas can begin. Horizontal wellbores are now frequently drilled within a productive formation to increase production rates and to recover greater quantities of hydrocarbons from the reservoir.
Sand or silt flowing into the wellbore from unconsolidated formations can lead to an accumulation of fill within the wellbore, reduced production rates and causing damage to subsurface production equipment. Migrating sand has the possibility of packing off around the subsurface production equipment, or may enter the production tubing and become carried into the production equipment. Due to its highly abrasive nature, sand contained within production streams can result in the erosion of tubing, flow lines, valves and processing equipment. The problems caused by sand production can significantly increase operational and maintenance expenses and can lead to a total loss of the well.
One means of controlling sand production is the placement of relatively large sand (i.e., “gravel”) around the exterior of a slotted, perforated, or other type liner or screen. The gravel serves as a filter to help assure that formation fines and sand do not migrate with the produced fluids into the wellbore. In a typical gravel pack completion, a screen is placed in the wellbore and positioned within the unconsolidated formation that is to be completed for production. The screen is typically connected to a tool that includes a production packer and a cross-over element, and the tool is in turn connected to a work or production tubing string. The gravel is mixed with a carrier fluid and is pumped as a slurry down the tubing and through the cross-over, thereby flowing into the annulus between the screen and the wellbore. The carrier fluid in the slurry leaks off into the formation and/or through the screen. The screen is designed to prevent the gravel in the slurry from flowing through it and entering the production tubing. As a result, the gravel is deposited in the annulus around the screen where it becomes tightly packed, forming a “gravel pack.” It is important to size the gravel for proper containment of the formation sand, and the screen must be designed in a manner to prevent the flow of the gravel through the screen.
Once the well has been completed and has been put into production, excessive fluid flow rates from any production zone can cause, among other things, excessive pressure drop between the formation and the screen. Experience has shown that the inflow distribution over the length of a horizontal well is rarely uniform. A problem that is sometimes encountered, especially in long horizontal sections, is an increased fluid flow rate at certain locations along the completed interval that leads to an increased risk of premature water or gas coning at these locations. When a well is produced, the natural flow characteristics of a uniform horizontal wellbore creates a pressure differential between the reservoir and the wellbore that increases significantly in the upstream direction. This is due to pressure losses from friction and turbulent flow within the production string. As a consequence of this increase in the differential pressure, the reservoir drainage rate will increase accordingly in the upstream direction. Thus the increased drainage around the “heel” of the wellbore can lead to excessive fluid production at this location and a less than optimum production rate for the rest of the horizontal wellbore. Other factors can lead to this lack of uniformity, including: varying permeabilities; the intersection of the wellbore with natural faults and fractures; the wellbore path wandering in and out of the reservoir; thin horizontal shale barriers; varying reservoir topography; and a non-uniform hydrocarbon distribution within the reservoir. An excessive production rate at the heel and/or at other locations can result in unwanted fluids prematurely coning to this location and entering the production stream. If there is a gas-oil contact or a water-oil contact near the wellbore, breakthrough will occur first at the point where the pressure drawdown is the highest.
To alleviate these problems, various methods for controlling the flow from various sections have been developed, including the use of external packers in conjunction with sliding sleeves or rotational port collars. Mechanical inflow control devices of varying designs have also been incorporated within the sand control screens to regulate the formation production rate along the horizontal wellbore. One design induces a pressure drop across a turbulent flow control device. These devices can comprise orifice restrictions, chokes, ported nipples or pressure compensated throttling device arrangements. Another design utilizes laminar capillary-tube flow controls such as helically placed tubing around the production string to impose a longer flow path, thus inducing an increased pressure drop. Some of these designs incorporate means for controlling the imposed restrictions and therefore the pressure drop can be altered at a later time if conditions require. All of the current available designs require significant modifications to the standard sand screen apparatus typically used in horizontal gravel pack completions and typically result in complex and expensive completions.
There is a need for improved apparatus and methods to enable the regulating and/or equalizing of the flow of produced fluids within horizontal gravel pack completions.